fix compatibility issues with ruby/gems in our test matrix

- faraday 2.9.0 dropped support for ruby 2.*, so we need to remove it from the test matrix
- rack 2.1.0 does not work with ruby 3.3, so it has been excluded from the test matrix
- faraday 1.10.3 works with ruby 3+, so we can remove the exclusion for it

.github/workflows/test.yml

@@ -1,20 +1,35 @@
 ---
 name: tests
-on: [ push, pull_request ]
+on: [push, pull_request]
 jobs:
   test:
     name: Test (Ruby ${{ matrix.ruby }} on ${{ matrix.gemfile }})
     runs-on: ubuntu-latest
     strategy:
       fail-fast: false
       matrix:
-        ruby: [ '2.6', '2.7', '3.0', '3.1', '3.2', '3.3' ]
-        gemfile: [ 'faraday_1.10.0', 'faraday_2.8.0', 'faraday_2.9.0', 'faraday_2.10.0', 'jwt_1.5.0', 'jwt_2.6.0', 'jwt_2.7.0', 'jwt_2.8.0', 'rack_2.1.0', 'rack_2.2.0', 'rack_3.0.0', 'rack_3.1.0' ]
+        ruby: ["2.6", "2.7", "3.0", "3.1", "3.2", "3.3"]
+        gemfile:
+          [
+            "faraday_1.10.0",
+            "faraday_2.8.0",
+            "faraday_2.9.0",
+            "faraday_2.10.0",
+            "jwt_1.5.0",
+            "jwt_2.6.0",
+            "jwt_2.7.0",
+            "jwt_2.8.0",
+            "rack_2.1.0",
+            "rack_2.2.0",
+            "rack_3.0.0",
+            "rack_3.1.0",
+          ]
         exclude:
-          - { ruby: '3.0', gemfile: 'faraday_1.10.0' }
-          - { ruby: '3.1', gemfile: 'faraday_1.10.0' }
-          - { ruby: '3.2', gemfile: 'faraday_1.10.0' }
-          - { ruby: '3.3', gemfile: 'faraday_1.10.0' }
+          - { ruby: "2.6", gemfile: "faraday_2.9.0" }
+          - { ruby: "2.7", gemfile: "faraday_2.9.0" }
+          - { ruby: "2.6", gemfile: "faraday_2.10.0" }
+          - { ruby: "2.7", gemfile: "faraday_2.10.0" }
+          - { ruby: "3.3", gemfile: "rack_2.1.0" }
 
     env: # $BUNDLE_GEMFILE must be set at the job level, so it is set for all steps
       BUNDLE_GEMFILE: ${{ github.workspace }}/gemfiles/${{ matrix.gemfile }}.gemfile